A device for characterizing the flow of a multiphase fluid flowing inside a tubing is described in documents FR-A-2 780 499 and FR-A-2 806 799. This device comprises several sets of electrodes positioned on the tubing, in such a way that the fluid flows between the electrodes. In such a device, the electrodes measure very weak currents and impedances. They should therefore not be in direct contact with the fluid and should be electrically insulated from the tubing. In addition, the fluid should be confined to flow through the middle of the group of electrodes. Therefore the latter should be an integral part of the tubing. However, the tubing in which measurements are performed often operate in environments such as are found in oil wells in which particularly harsh conditions prevail. For example, the temperature may attain several hundred degrees and the pressure may be larger than 1,000 bar in an environment containing H2S. The device for integrating the electrodes into the tubing should there fore withstand such conditions without reducing the internal diameter of the tubing.